Protein phosphorylation has evolved as the most versatile posttranslational modification used by cells. A broad spectrum of cellular processes, including gene expression, development and cell division are tightly regulated by phosphorylation. Although structure/function analysis of mammalian phosphorylation components is difficult due to the complex nature of the diploid genome, vaccinia virus encodes two protein kinases (B1 and F10) and a protein phosphatase (H1), providing a more manipulatable genetic system. The B1 kinase has been intimately linked with viral genome replication, however the underlying mechanism(s) by which it acts remains elusive. Recently, a number of newly identified putative mammalian kinases, have been described which bear striking resemblance to the B1 kinase. The goal of this proposal is to perform structure/function analysis on these cellular and viral kinases to examine if and how these kinases are related; to use this information to further our knowledge as to the pathogenesis of vaccinia and to provide new insights into the complex network of protein kinases that regulate cellular processes.